1. Field of the invention
The present invention relates to a dielectric ceramic composition and, more particularly, a high permittivity dielectric ceramic composition.
2. Description of the prior art
As a high permittivity dielectric ceramic material for capacitors, there have widely been used dielectric ceramic compositions of a system BaTiO.sub.3. Other dielectric materials presently used are compositions of a system, SrTiO.sub.3 -PbTiO.sub.3 -Bi.sub.2 O.sub.3 TiO.sub.2 or SrTiO.sub.3 -PbTiO.sub.3 -Bi.sub.2 O.sub.3 -TiO.sub.2 -CaTiO.sub.3. Such compositions are disclosed in Japanese patent lay-open No. 52-41880 or U.S. Pat. No. 3869398.
However, the composition of the BaTiO.sub.3 system gives a high distortion factor when applied to ceramic capacitors. For example, the composition gives values for third harmonic distortion of -50 to -75 dB when it is applied with a voltage of 10 to 50 Vrms/mm.
On the other hand, the composition of the system SrTiO.sub.3 -PbTiO.sub.3 -Bi.sub.2 O.sub.3 -TiO.sub.2 or SrTiO.sub.3 -PbTiO.sub.3 -Bi.sub.2 O.sub.3 -TiO.sub.2 -CaTiO.sub.3 makes it possible to produce capacitors with a value of third harmonic distortion smaller than that of the BaTiO.sub.3 compositions. However, such a composition has a large dependency of distortion factor on AC voltage, as compared with other capacitors such as film capacitors and aluminum electrolyte capacitors. In addition, when such a composition is applied to multilayer-layer ceramic capacitors, it is required to use noble metals such as platinum as a material for internal electrodes because of high sintering temperature of the composition of 1300.degree. to 1350.degree. C. The use of noble metals results in increase of the manufacturing cost of capacitors.